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Hot Water Report

Hot Water Report 2025: Issue 6

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INTRODUCTION: 
The 2025 Hot Water Report provides real-time data in the lower Snake and Columbia river reservoirs to detail the collective impacts of hot, stagnant, and toxic waters on already-imperiled salmon and steelhead. 

EXECUTIVE SUMMARY:

  1. Hot water temperatures in the lower Snake and Columbia rivers: Many of the reservoirs behind the lower Snake and Columbia River dams have experienced more than 80 days of water temperatures exceeding the 68°F “harm threshold” set to protect migrating salmon and steelhead. 
    • Highest water temperature in the lower Snake River: On August 17, Ice Harbor Dam’s reservoir registered the highest water temperature of 72.95°F – nearly 5°F above the 68°F “harm” threshold.
    • Total days above 68°F in the lower Snake River: Ice Harbor reservoir has been above 68°F for the longest at 89 consecutive days. 
    • Read current water temperatures in the lower Columbia and Snake rivers here. 
  2. Toxic water in the lower Snake River: For the third consecutive year, toxic algal blooms with microcystins (a liver toxin) have been detected in the lower Snake River. Toxic algal bloom health advisories remain in effect today.
  3. On the brink of extinction: The status of salmon, steelhead, and Southern Resident orcas: Despite billions of dollars and decades of efforts to restore Southern Residents and salmon, they both teeter on the brink of extinction today:
    • Status of Salmon and Steelhead: Idaho Rivers United recently published their Wild Salmon and Steelhead Returns Report, including adult Spring/Summer Chinook, Steelhead, and Sockeye returns as of 9/15/25. The report shows Snake River salmon and steelhead return annually far below the recovery goals necessary to remove them from the protections of the Endangered Species Act and to achieve region-wide goals.
    • Status of Southern Resident Orcas: Southern Resident orcas, listed as endangered in both the U.S. and Canada, have only 74 individuals surviving (according to the Center for Whale Research’s annual census of the Southern Resident population completed in July 2025). The recent tragic deaths of several orcas underscore the continuing need for abundant salmon throughout the range of the Southern Residents and on a year-round basis. Restoring abundant salmon populations in the Snake River Basin is an essential ingredient for successful recovery.

WATER TEMPERATURE DATA FOR LOWER SNAKE AND COLUMBIA RIVERS

Introduction to the water temperature data: The daily average and high water temperature data at the eight reservoir forebays are measured with sensors stationed at various depths below the reservoir surface, immediately upstream from the dams.

LOWER SNAKE RIVER WATER TEMPERATURE DATA 

Click here to view the lower Snake River water temperatures - 2025 Daily Average and 10-year Average.

Average water temperature:  Between July 1 - September 29, the highest daily average temperature across all four lower Snake reservoirs was at Ice Harbor reservoir, averaging 72.64°F on August 17.

Highest water temperature: On August 17, Ice Harbor Dam’s reservoir registered the highest water temperature of 72.95°F – nearly 5°F above the 68°F “harm” threshold.

Total days above 68°F in the lower Snake River: Ice Harbor reservoir has been above 68°F for the longest at 89 consecutive days.

LOWER COLUMBIA RIVER WATER TEMPERATURE DATA 

Click here to view the lower Columbia River water temperatures - 2025 Daily Average and 10-year Average.

Average water temperature: Between July 1 - September 29, John Day reservoir had the highest daily average temperature at 73.76°F on September 6.

Highest water temperature: On August 28, the John Day reservoir registered the highest water temperature of 74.48°F – over 6 degrees above the 68°F “harm” threshold.

Hot Water Temperatures and Toxic Algal Blooms in the Lower Snake River

Today, Snake River salmon and steelhead face dramatically decreased survival rates, largely due to the federal system of dams and reservoirs in the Columbia River Basin. The dams on the lower Snake River in southeast Washington State—Ice Harbor, Lower Monumental, Little Goose, and Lower Granite—and their stagnant reservoirs heat up this historic, once highly productive river, harming and killing both juvenile and adult fish.

How do the dams impact water temperatures? The lower Snake River dams create stagnant reservoirs - large, slow-moving pools that absorb enormous amounts of solar radiation and cause water temperature to reach lethally high levels. The reservoirs warm during the summer months and create a block (barrier) of hot slow-moving water that retains the heat through the night and does not cool until air temperatures remain low in the fall. Fish ladders, the only route past the dams for adult fish, also frequently contain warm surface waters that are hotter than the average river temperature, and such conditions create and exacerbate migration blockages. These blockages prevent successful migration to spawning grounds and attract predators, thereby reducing the survival and reproduction of salmon.

High Water Temperatures in 2025: All lower Columbia and Snake River dams and their reservoirs have reached water temperatures above 68°F – above the biological and legal threshold scientists identified to protect salmon from lethal water temperatures. Endangered Snake River fish migrate through a total of eight dangerously hot and stagnant reservoirs on their migration to the ocean as juveniles and again on their journey back upstream as adults. Depending on salmon species, migration for salmon and steelhead stops altogether when water temperatures reach 72-73°F. Salmon that have stopped or slowed their migration can languish for days or weeks in warm water and die from thermal stress and disease.

Salmon and steelhead are highly resilient. They can tolerate episodes of warm water, but they have limits on how long and how much hot water they can withstand. The cumulative impact of hot reservoirs in the lower Columbia and the lower Snake must be addressed quickly - to reduce water temperatures and the overall exposure time for these fish to waters above 68°F.

Emergency fishing closures: The warming water temperatures that occurred this fall in the Columbia and Snake rivers impacted the behavior and survival of fall Chinook and steelhead by significantly delaying their migration into Idaho. As a result of warming waters slowing fall Chinook migration and causing a reduction in the number of fish reaching northeast Oregon and Idaho, adult fall Chinook salmon fisheries in the Snake River were closed from Sept. 19 to Oct.4.

Toxic algal blooms: For the third consecutive year, toxic algal blooms with microcystins have been detected in the lower Snake River. Microcystin is a liver toxin that can pose a significant health risk if ingested, inhaled, or upon skin contact. The warm and stagnant water conditions created by the dams allow toxic algal blooms to grow, making the river sick, unsafe, and dangerous for people, pets, and already endangered salmon and steelhead. Already under stress due to warm reservoir temperatures, salmon and steelhead must also migrate through toxic algal blooms that can cause oxygen depletion and changes in pH levels. 

Below are confirmed toxic algal blooms present in the lower Snake River and Snake River region (as of October 6, 2025): 

Toxic algal bloom Oct 2025

TOXIC ALGAL BLOOMS IN THE LOWER SNAKE RIVER

TOXIC ALGAL BLOOMS IN THE SNAKE RIVER (between Oregon and Idaho):

ON THE BRINK OF EXTINCTION: THE STATUS OF SALMON, STEELHEAD, AND SOUTHERN RESIDENTS

Status of Snake River salmon and steelhead:

Wild Salmon and Steelhead Returns Report by Idaho Rivers United 
Click here to view the full report.

Sources: Fish Passage Center, Idaho Department of Fish and Game, and the Columbia Basin Partnership (CBP)

The Wild Salmon and Steelhead Returns Report by Idaho Rivers United shares returns as of 9/15/25:

  • Historical returns: The report includes historic Snake River salmon and steelhead population numbers as a critical reminder that the Snake Basin once supported millions of returning salmon and steelhead, and how diminished current numbers are today, as seen in the graphs outlining yearly returns.
  • Yearly returns: The graphs show annual return numbers for various runs of Snake River fish, some of which are currently in-season. They also give important context with population estimates immediately pre-lower Snake River Dams. These populations from the mid-20th century represented abundant, harvestable numbers of wild fish, and recovery to these levels is possible in the future thanks to the high-quality habitat upstream from the dams.
  • Current returns: Snake River sockeye are listed as “endangered” – the most severely imperiled ESA status. As of 9/15/25, just 14 wild/natural sockeye salmon have returned to the Stanley Basin in Central Idaho.
  • Quasi-extinction threshold: “Salmon runs have plummeted since the signing of the treaties and reservation executive orders that would protect the Tribes’ harvest rights.[...] wild-origin returns of salmon to the Snake Basin are 0.1-2% of their historical abundance, with many populations at or below a quasi-extinction threshold,” states the Department of Interior’s Historic and Ongoing Impacts of Federal Dams on the Columbia River Basin Tribes Analysis. A quasi-extinction threshold (QET) signifies 50 spawners or less in a salmon or steelhead sub-population, and is a sign of near-term extinction. After the QET threshold is passed, the probability of recovery is low without substantial and immediate intervention.
  • Recovery Goals: Snake Basin recovery goals were developed by fisheries managers and stakeholders in the Columbia Basin Partnership Phase II Report, and represent healthy and harvestable levels of abundance. The goals displayed on the graphs above are for populations returning to currently accessible habitat. Snake River salmon and steelhead populations are currently far below these high-end recovery targets, as well as the thresholds necessary for ESA delisting.

Status of Southern Residents: 

Southern Residents are the original fishers of the Pacific Northwest waters, co-evolving over millennia with their preferred prey, Chinook salmon. However, Southern Resident orcas are listed as endangered in both the U.S. and Canada, with only 74 individual Southern Resident orcas surviving (according to the Center for Whale Research’s annual census of the Southern Resident population completed in July 2025).

There have been many losses of Southern Resident calves and the outward grief that the Southern residents express:

On December 31st, 2024, 27-year-old J35 Tahlequah was seen carrying a dead female neonate calf in the Salish Sea. She continued to carry the calf for several more days, reminiscent of her 17-day Tour of Grief in 2018.

On September 12th, 2025, 26-year-old J36 Alki was documented by the Center for Whale Research carrying a dead female neonate calf with its umbilical cord still attached. This was not her first loss. Alki’s 2-year-old son J52 Sonic died in 2017, and she has experienced multiple miscarriages since then.

Less than a week later, a brand-new calf was spotted in the J16 matriline. Alki’s sister, 18-year-old J42 Echo, is the presumed mother, which was certainly welcome of bittersweet news. Meanwhile, J62 and J63, born last winter, appear to be doing well.

Columbia-Snake River Basin salmon importance to Southern Resident orcas:

We cannot know for certain the exact cause of death of these two calves, while others born to J Pod in the past year have survived. But we do know that the persistent lack of salmon on a year-round basis is the single greatest threat to Southern Residents' survival. Snake River Spring/Summer Chinook and Snake River Fall Chinook as well as many Columbia-Basin salmon runs are ranked in the top 10 Priority Chinook stocks for orca recovery. The Southern Residents are experiencing a very high rate of miscarriage, primarily due to low availability of salmon.

Despite billions of dollars and decades of efforts to protect and restore Southern Residents and salmon, they both teeter on the brink of extinction today. Both the successful births and tragic deaths underscore the urgent need for abundant salmon throughout the range of the Southern Residents on a year-round basis. Restoring healthy salmon populations in the Snake River is an essential component for successful recovery.

Learn more about the status of Southern Resident orcas and the latest research on recovering endangered Southern Residents informed by Bigg’s orcas' recovery journey, from the research of Orca Behavior Institute with reports from Pacific Whale Watch Association, and Orca Network.

Read more about Center for Whale Research’s annual census of the Southern Resident population here and on the recent Seattle Times article, "Southern resident K pod falls to lowest number since counts began."

Recovering Healthy, Abundant, and Harvestable Salmon and Steelhead Populations: 

Endangered sockeye salmon in Redfish Lake - 900 miles inland and 6500 feet above sea level. © Emily Nuchols

The Snake and Columbia River Basins contain some of the very best available habitat for salmon populations to recover to any significant level of abundance. We can recover healthy and abundant salmon populations, restore resilient rivers and streams that these fish depend upon in the Columbia-Snake Basin, and ensure a more prosperous future for all people and communities. As Jeremy Takala, Chair, Columbia River Inter-Tribal Fish Commission, states, “We must restore Columbia Basin fisheries to healthy and abundant levels. The economic and ecological health of our region requires it, and tribal treaty rights demand it.”

With this continuing crisis in the lower Snake River, and many Columbia-Snake River salmon and steelhead populations facing extinction, the “Six Sovereigns” — Confederated Tribes of the Umatilla Indian Reservation, Confederated Tribes of the Warm Springs Reservation of Oregon, the Confederated Tribes and Bands of the Yakama Nation, Nez Perce Tribe, State of Oregon, and State of Washington — jointly developed in 2023 the Columbia Basin Restoration Initiative (CBRI). It is a comprehensive, science-based, and durable strategy to restore salmon and other native fish populations to healthy and abundant levels, ensure a clean energy future, support local and regional economic and climate resilience, restore ecosystem function, and honor longstanding unmet commitments to Tribal Nations.

Restoring a free-flowing lower Snake River is one essential strategy to provide a critical cold-water refuge that salmon and steelhead have historically relied upon to rest and recover during their long upstream migration. It can also dramatically reduce the incidence of toxic algal blooms. Restoring a free-flowing river has proven to benefit the ecosystem, fish, and people. NewsData recently focused attention on the Klamath River’s first year as a free-flowing river. It found that scientists are already seeing dramatic changes in average daily water temperatures in the stretch of river. “We’re just opening up that river to be free-flowing, and basically just allowing it to do its normal hydrological things: scour the river, help with fish disease, help with the temperature aspect and get rid of blue-green algae,” said Crystal Robinson, Klamath Watershed program manager for the California Department of Fish and Wildlife.

Salmon and steelhead—and endangered Southern Resident orcas and other fish and wildlife that depend on salmon—are running out of time. At this moment, we have an urgent need to restore ecosystem health, improve resilience and recover salmon and steelhead by removing the four lower Snake River dams and replacing the dams’ services. By protecting the Northwest's native fish from extinction, we will help to uphold our nation's promises to Treaty Tribes and reconnect this emblematic fish to 5,500 miles of pristine, protected river and streams in Idaho, Oregon, and Washington. This is our greatest river/salmon restoration opportunity anywhere on the West Coast.

FURTHER INFORMATION: 

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Data Sources: The 2025 water temperature data for the lower Snake River and lower Columbia River presented in the Hot Water Report are collected from the USGS, and the Columbia River DART program by Columbia Basin Research, University of Washington, with data courtesy of the U.S. Army Corps of Engineers (USACE). These data temperatures are provisional. The 10-year average water temperature data is courtesy of the Fish Passage Center. There is no data available for the Lower Monumental 10-year average water temperature. Graphs and tables are assembled by SOS Staff.

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